Well pumping equipment

ABSTRACT

A well pumping equipment comprises a pump (1) with an electric motor (2), each having its body suitable for location in a well using a tubing (3), a frequency converter (4) electrically coupled by a cable (5) to the electric motor (2) and including a rectifier (6) and inverter (7). The inverter (7) is adapted to be located in the well and is connected to the rectifier (6) by a single-conductor cable (5), while the other single-conductor connection line to supply power to the electric motor (2) and the inverter (7) is the electric connection of the motor (2) and inverter (7) bodies with the tubing (3).

FIELD OF THE INVENTION

The present invention relates to production of oil and other formationfluids, and can be employed in submersible electric pumping.

BACKGROUND OF THE INVENTION

Known in the art is a submersible pump assembly comprising an electricmotor having an electromechanical transducer shaft connected to a pumpshaft, and a frequency converter electrically coupled to the electricmotor (PCT, A1, WO 91/19905).

In this assembly, the converter is arranged in the area of the electricmotor mount and is suitable for location with the submersible pumpassembly directly in the well.

The problem with the pump assembly above is that a three-conductor cableshould be used to supply power to the electric motor and the frequencyconverter. It makes the assembly less reliable and raises its operatingcost, in particular, when the submersible pump assembly operates in thewells at large depths.

A well pumping system disclosed in Maximov V. P. "Adjustable Control ofSubmersible Pump System Drive", Moscow, 1981, pages 5,6, comprises apump with an electric motor, each having its body suitable for locationin a well using a tubing, and a frequency converter electrically coupledby a cable to the electric motor, the frequency converter including arectifier and an inverter.

In this pump system, the frequency converter is located at the daylightsurface in the vicinity of the well mouth and is connected by amulticore cable to the electric motor. In this case, voltage is alsodelivered to the electric motor by a three-conductor cable whoseinsulation has to meet stringent requirements. This raises the operatingcosts since the cable conductors are made of copper in order to providethe adequate electric connection, and failure of the insulation betweenthe conductors may cause the risk of the system damage.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a well pumpingequipment wherein the frequency converter design and connection to theelectric motor permits the employment of a single-conductor cable tosupply power to the submersible pump, ensuring thereby the reduction inthe amount of metal per structure and making the equipment more costeffective and reliable.

The aforementioned object is attained by a well pumping equipmentcomprising a pump with an electric motor, each having its body suitablefor location in the well using a tubing, a frequency converterelectrically coupled by a cable to the electric motor and including arectifier and inverter, wherein in accordance with the invention theinverter is adapted to be located in the well, an input bus of theinverter being connected to a first output bus of the rectifier by asingle-conductor cable, while the other singleconductor connection lineto supply power to the electric motor and the inverter is the electricconnection of the motor and inverter bodies with the tubing which iselectrically coupled to a second output bus of the rectifier.

The above features and advantages of the present invention will beapparent from the following description of its best embodiment, token inconjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view of a well pumping equipment of the presentinvention.

DESCRIPTION OF THE BEST EMBODIMENT OF THE INVENTION

Referring to FIG. 1, a well pumping equipment comprises a pump 1 with anelectric motor 2, each having its body suitable for location in a wellusing a tubing 3, a frequency converter 4 electrically coupled to theelectric motor 2 by a cable 5 and including a rectifier 6 and aninverter 7. In accordance with the invention, the inverter 7 is adaptedto be located in the well and is coupled to a first output bus of therectifier 6 by a single-conductor cable 5, while the othersingle-conductor connection line to supply power to the electric motor 2and to the inverter 7 is the electric connection from the electric motor2 and inverter 7 bodies to the tubing 3 which is electrically coupled toa second output bus of the rectifier 6.

In addition, FIG. 1 schematically depicts a lifting pipe string 8 and adaylight surface 9, and control units commonly used in the systems toperform specific functions, which are known in the art and do not formthe subject matter of the present invention, such as a rectifier controlunit I0, a transformer 11 and a control station 12.

A well pump equipment in accordance with the invention operates asfollows.

A three-phase supply current voltage with a frequency of 50Hz, deliveredfrom a control station 12, is converted by a transformer 11 into anominal voltage required to operate an electric motor 2, e.g. 750 V to2300 V, depending on the electric motor 2 power. The nominal voltage isfed to an input of a frequency converter 4 which converts the 50 Hzfrequency voltage into the voltage of the same magnitude with thefrequency spectrum adjustable in the range from 0 Hz to 100 Hz. Directvoltage from a rectifier 6 is supplied over a single-conductor cable 5to an input of an inverter 7. The inverter 7 converts themagnitude-controlled direct voltage into the frequency-controlledalternating voltage and feeds it to an input of the electric motor 2 sothat to start up the electric motor 2 at the supply voltage frequencyrequired for particular operating conditions of the pump.

Owing to removing the inverter 7 from the part of the frequencyconverter 4, arranged at the daylight surface, and locating it in theimmediate vicinity of the electric motor 2, power can be supplied to theinverter 7 by a single-conductor cable, while the tubing 3 is the othersingle-conductor connection line to supply power. The above arrangementof the inverter 7 eliminates the risk of damage caused by distractingthe insulation between the conductors of the multicore cable, reducesthe amount of metal per structure, improves the equipment costefficiency owing to the smaller electric losses and the reduction innumber of copper conductors from three to a single one, and enhancesreliability owing to the reduced number of electric connections whichmost frequently fail in practice due to great distances run by the cable5.

Industrial Applicability

A well pump equipment in accordance with the present invention is mostlyuseful in oil production, particularly, it can be employed to producewells having considerable depths.

What is claimed is:
 1. A well pumping equipment comprising a pump withan electric motor, each having its body suitable for location in a wellusing a tubing, a frequency converter electrically coupled by a cable tothe electric motor, the frequency converter including a rectifier and aninverter, characterized in that the inverter is adapted to be located inthe well, an input bus of the inverter being connected to a first outputbus of the rectifier by a single-conductor cable, while the othersingle-conductor connection line for supplying power to the electricmotor and the inverter is the electric connection of the motor andinverter bodies with the tubing which is electrically coupled to asecond output bus of the rectifier.
 2. A well pumping apparatuscomprising:a pump sized to fit within an electrically conducting welltubing and comprising a multiphase electric motor mechanically linked toa pump; a frequency converter comprising a rectifier operatively coupledto a source of AC voltage and having a first output for providing DCvoltage and a second output electrically coupled to the well tubing, andan inverter operatively coupled to the electric motor, the inverterhaving an input and an output wherein the inverter is adapted to belocated in the well tubing; and a single conductor cable coupled to thefirst output of the rectifier and the input of the inverter whereby DCvoltage delivered from the first output of the rectifier by the cable tothe input of the inverter is converted to multiphase AC voltage for useby the motor.